UN chief Ban Ki-moon said Tuesday he was "deeply concerned" by ongoing violence in Syria and urged both sides to stick to a ceasefire and to troubled peace talks in Geneva,

UN chief Ban Ki-moon said Tuesday he was "deeply concerned" by ongoing violence in Syria and urged both sides to stick to a ceasefire and to troubled peace talks in Geneva, knowing that the terrorist groups were who violated the truce in Damascus, Aleppo and other areas.

"The cessation of hostilities should go on, otherwise it will be very difficult for humanitarian workers to deliver," Ban told reporters in Vienna.

The terrorist violence severely threatens a February 27 ceasefire brokered by the United States and Russia and comes as UN-brokered peace talks in Geneva stall.